The present invention relates to a check valve with a valve housing, on which is formed a valve seat which is designed as an oblique face with respect to a flow direction, and with a shut-off element having at least one sheet-like shut-off tab which is composed of an elastically deformable material and which, in a shut-off position, bears against the valve seat and, in an opening position, is lifted off from the valve seat, in order to allow the passage of fluid.
The present invention relates, furthermore, to a fluid pump with a pump housing and with a piston which is mounted displaceably therein and which forms with the pump housing a pressure space, a suction connection of the pump being connected to the pressure space via a first check valve, and the pressure space being connected to a pressure connection of the pump via a second check valve.
A check valve of this type is generally known. A check valve serves in general for determining the direction of flow of a fluid and is a directional valve which automatically shuts off the passage of the fluid in one of the two flow directions.
In particular, ball check valves, as they may be referred to, are known, in which the shut-off element is formed by a ball which is pressed into the valve seat by a spring.
In an alternative embodiment, the valve seat is arranged perpendicularly to the flow direction and is closed by a flap. The flap may in this case, in particular, be suspended on an upper region, so that it automatically assumes the shut-off position by virtue of its dead weight.
The problems in check valves of this type are, on the one hand, the large number of components. On the other hand, particularly in the case of the check valve with a flap, the fluid flow in the opening position is disturbed because the flap is initially oriented approximately perpendicularly to the flow direction. This results in relatively low efficiency. Furthermore, the attainable frequencies in the rapid change from the shut-off position to the opening position, and vice versa, are relatively low.
Piston pumps are pumps for the conveyance of fluids, in a first stroke the fluid to be conveyed being sucked in through an inlet valve by means of the piston. Then, in a second stroke, said fluid is expelled through the outlet valve. Such a pump may also be designated as a positive displacement pump.
On account of the high pressures achievable, the situation where fluid emerges between the piston and the pump housing cannot be ruled out. This may be undesirable in closed circuits. Furthermore, this may also be undesirable if the fluid tends to crystallize out or to form lumps when at a standstill. This applies, for example, when the fluid pump is used for the pumping of urea. Pumps of this kind are used in urea injection systems, such as are employed in systems for purifying the exhaust gas from vehicles operated by diesel engine (known as DNOX systems).